"The IRS gave 5 items that may have caused disallowance"

The payments are Advances based on the tax returns on file.

In the 2021 filing, "could be a dependent" is also one of the items. Just because you file your own return and have a filing requirement, you are still supposed to show if you could be claimed or not by another taxpayer.

If she got the advance payment and now the parents state she is their dependent, then she should not have gotten the payment, which was for 2021. The point being, one payment has been made in advance, so there is no further amount to be paid.

Did you want to fight to get a second payment?

If the family is mad, shouldn't they fight among themselves?